1. Technical Field
The present technology relates to a pneumatic tire, and particularly relates to a pneumatic tire in which, when applied air pressure is increased to reduce rolling resistance for the purpose of improving fuel efficiency, wear in a center region and worsening of dry braking ability caused by an increase in ground contact pressure that accompanies an increase in radial growth of the center region are improved.
2. Related Art
Conventionally, pneumatic tires are known in which a curvature of a profile along a tire width direction of a tread surface is close to a straight line (e.g. see Japanese Unexamined Patent Application Publication No. 2008-307948). Such a pneumatic tire has a plurality of arcs having different curvature radii in a tread surface, including at least a center portion arc positioned in a center in the tire width direction and a shoulder side arc positioned outermost in the tire width direction. When a cross-section in a tire meridian direction is viewed in a state where the pneumatic tire is assembled on a regular rim and is inflated to an inner pressure that is 5% of a regular inner pressure; an intersection of an imaginary extended line that is parallel to a tire radial direction and extends from a position outermost in the width direction toward an outer circumferential side in the tire radial direction of a belt layer and a profile of the tread surface is a reference point; an intersection of a tire equatorial plane and the profile of the tread surface is a center crown; an angle formed by a line joining the reference point and the center crown and a line parallel to the tire width direction is θ; a curvature radius of a center portion arc is Rc; a curvature radius of a shoulder side arc is Rs; a reference developed width that is an arc length from the tire equatorial plane to a position at an edge of the shoulder side arc on the tire width direction inner side is L; and a developed tread width that is an arc length of the tread surface in the tire width direction is TDW, the tread surface is formed so as to satisfy 1°<θ<4.5°, 5<Rc/Rs<10, and 0.4<L/(TDW/2)<0.7.
In recent years, research has been conducted into increasing applied air pressure to reduce rolling resistance of a pneumatic tire for the purpose of improving the fuel efficiency of a vehicle on which the pneumatic tire is mounted. However, increasing the applied air pressure leads to an increase in radial growth of a center region (center in the tire width direction). An increase in ground contact pressure of the center region accompanies the increase in radial growth thereof, which results in the center region of the tread surface becoming prone to wear.
With the pneumatic tire described in Japanese Unexamined Patent Application Publication No. 2008-307948, wear in the center region of the tread surface tends to be improved by making a curvature of the profile along the tire width direction of the tread surface close to a straight line. However, when the pneumatic tire described in Japanese Unexamined Patent Application Publication No. 2008-307948 is highly pressurized, unevenness of wear of the pneumatic tire cannot be sufficiently suppressed. Moreover, depending on the shape thereof, rolling resistance of the pneumatic tire cannot be appropriately reduced.